Automatic tripper for belt conveyors



Jan. 10, 1956' M. s. GREELEY ETAL 2,730,228

A TOMATIC TRIPPER FOR BELT CONVEYORS Filed March 19, 1952 4 Sheets-Sheetl HTTGRNE Y5 AUTOMATIC TRIPPER FOR BELT CONVEYORS Filed March 19, 1952 4Sheets-Sheet 2 INVENTORS. MAWK 5. GREELE) T2} 2 wkw HTT'OANEYS 1956 M.s. GREELEY ETAL A TOMATIC TRIPPER FOR BELT CONVEYORS 4 Sheets-Sheet 5Filed March 19, 1952 m w? m mrv v w 5 r mv 9 Z 0 M 1911- 1956 M. s.GREELEY ETAL A TOMATIC TRIPPER F OR BELT CONVEYORS 4 Sheets-Sheet 4Filed March 19, 1952 INVENTORS. MAWA 5. GKEELE) BY Ruff/TON a. K/MBKOfirm/mars United States Patent Mark S. Greeley and Rushton 0.

Ala, assignors to Continentai Gin Company, a corporation of DelawareApplication March 19, 1952, Serial No. 277,468 12 Claims. (Cl. 198186)This invention relates to an automatic tripper for belt conveyors andhas for an object the provision of .fluid pressure means for propelling,movement of the tripper.

Another object of our invention is to provide an automatic fluidpressure actuated belt conveyor tripper embodying improved means foractuating a rail gripping brake member in event there is a pressurefailure or a break in the hydraulic or pneumatic lines.

Another object of our invention is to provide an automatic tripper ofthe character designated having reversing means incorporated therewithwhich shall be operated by adjustable limit means positioned along thetrack upon which the tripper moves.

A further object of our invention is to provide a fluid pressureactuated tripper having associated therewith braking means adapted to beenergized upon contact with a stationary member positioned along thetrack upon which the tripper moves, thus limiting the distance thetripper will move along the track and preventing the tripper fromgetting out of control when there is a pressure failure, or in any partof the tripper.

A more specific object of our invention is to provide an automatictripper of the character designated including means for regulating thepressure in the hydraulic or penumatic lines, thus keeping a constantpressure in the lines at all times, and including means forautomatically stopping the tripper in event the pressure falls below apredetermined amount.

Heretofore in the art to which our invention relates, trippers have beenpropelled either mechanically or electrically. The mechanical type isusually propelled by coupling power from the conveyor belt through thetrip per head and bend shafts and a clutching system to the tripperaxle, or by an arrangement of friction wheels on the head and bendshafts coupled to the tripper axle. In order to operate such systemsautomatically a series of levers, cams, links and weights, are used toengage one clutch and at the same time disengage another. Accordingly,there are several adjustments that must be made and maintained in orderto obtain satisfactory operation since the wearing of the clutch facingconstantly changes these adjustments. Furthermore, since the operationis usually of a trigger action type, close maintenance is necessary inorder to keep all the mechanism in operating condition. When theclutches are both in a neutral position the tripper is a free rollingbody, and the belt has a tendency to roll the tripper toward theconveyor head pulley. The tripper thus gains velocity in the directionof belt travel, approaching the belt speed as a limit. The same actionresults when a belt hangs in any part of the tripper, such as resultsfrom a broken pulley shaft. Run-away trippers have in the past causedconsiderable damage to installations.

While electrically operated trippers have been satisfactory inoperation, the electric power must be fed to them either by trolleysorby an automatic cable reel. Aninthe event the conveyor belt hangs instopping and reversing the i stallation of this type is much moreexpensive than the mechanically operated type. Also sparking of trolleysand reel brushes are a hazard in some installations, thus preventingthis type of tripper from being accepted for all types of installations.Furthermore, the electric type trippers, so far as we are aware, areprovided with no means for preventing the tripper from being draggedalong its track by thebelt in the event a shaft is broken, or if for anyreason the belt should become fastened to the tripper.

We overcome the above mentioned difliculties by providing automatichydraulic or pneumatic means for propelling, stopping and reversing thetripper as it moves along its tracks.

Briefly our invention comprises means for taking the propelling powerdirectly from the conveyor belt. The power taken from the conveyor beltis utilized to drive a fluid pressure pump which may be either ahydraulic or pneumatic pump and which in turn provides fluid underpressure for propelling a fluid pressure motor. The motor is operativelyconnected to an axle of the tripper, thereby driving the tripper alongits track. The reversal of the tripper is obtained by mounting afour-way pilot valve on the tripper in position to engage a stationaryprojecting member positioned along the side of the track upon which thetripper moves. The pilot valve reverses the direction of movement of thetripper by reversing the direction of flow of the fluid through themotor. Our tripper also includes a braking member which is operable uponrelease of pressure in the pressure system or when the tripper passesbeyond a predetermined point along the track.

Apparatus embodying features of our invention is illustrated in theaccompanying drawings forming a part of this application in which:

Fig. l is a side elevational view of the tripper partly broken away andin section;

Fig. 2 is a plan view thereof partly broken away and in section andshowing the belt removed;

Fig. 3 is a front elevational view thereof;

Fig 4 is a diagrammatic view showing the hydraulic or pneumatic pressurelines employed and the means for braking the tripper;

Fig. 5 is a detailed view taken generally along the lines VV of Fig. 4;and,

Figs. 6 and 7 are detail sectional views of the four-way pilot valve.

Referring now to the drawings for a better understanding of ourinvention, we show a tripper frame indicated generally by the numeral10. The frame is mounted on wheels 11 which travel along tracks 12.Mounted for rotation adjacent the upper forward end of the frame 10 andextending transversely thereacross is an upper shaft 13 having securedthereto a pulley 14. Mounted for rotation on, and extending transverselyacross, the frame 10 at a point inwardly of and below the shaft 13, is abend shaft 16, having secured thereto a pulley 17. Passing around thepulleys 14 and 17 and having a reverse lapportion therein is a conveyorbelt 18, which is employed to convey any suitable material, such ascoal, sand, gravel, limestone, and the like. The material to be conveyedis indicated generally at 19 and is transported to the conveyor belt 18by a second belt 20. Secured to the forward end of the tripper frame 10is a suitable hopper 21 arranged to receive the material conveyed by thebelt 18 and adapted to discharge the same into a suitable" bin or binsat the sides of the track 12 or back onto the belt for discharge overthe head end. The shaft 13 is rotably mounted in suitable bearings 22and the shaft 16 is rotatably mounted in suitable bearings 23.

Secured to the bend shaft 16 and spaced laterally of the pulley 17 is asprocket 24. Mounted for rotation on the frame above the bend shaft 16in bearings is a counter-shaft 26 having secured thereto a sprocket 27.The sprockets 24 and 27 the connected by means of a drive chain 28.Sprocket 24 is larger in diameter than sprocket 27, thus causing thecounter-shaft 26 to rotate at a higher speed than the bend shaft 16.Also secured to the counter-shaft 26 is a sprocket 29. Mounted on theframe 10 rearwardly of the counter-shaft26 is a fluid pressure pump 31havinga drive shaft 32. For the purpose of this description the pump 31is shown as a hydraulic pump. Secured to the shaft 32 is a sprocket 33driven from the sprocket 29 through a drive chain 34. As shown in Fig.1, the sprocket 33 is smaller in 7 diameter than the sprocket 29, thuscausing the pump drive shaft 32 to be driven at a higher speed than thecounter-shaft 26. A By providing these speed increases between the shaft16 and the shaft 26 and between shaft 26 and shaft 32, we are enabled toemploy conventional types of hydraulic pumps which must run at arelatively higher speed than the tripper bend shaft 16.

The iii-take side of the hydraulic pump 31 communicates with a reservoiror tank 36 by means of a pipe 37. The

out-put side of the hydraulic pump 31 communicates with a pressurerelief valve 38 of any well known design. by means of a pipe 39. Thepressure relief valve 38 is set at a predetermined operating pressure sothat the hydraulic pump maintains a pressure equal substantially to thepressure built up when the tripper is moving along the track with thebelt 18, which is the lowest speed of the pump 31. When the tripper ismoving along the track 12 opposite the direction of belt travel, thepump 31 operates at a higher speed, but the pressure relief valve 38by-passes the excess fluid to the reservoir 36 through pipe 35, therebyholding the hydraulic operating circuit at a constant pressure in bothdirections of tripper travel.

The pump 31 delivers fluid under pressure through the valve 38 and apipe 41 to a four-way pilot operated valve 42, of any well knowndesign.Mounted on the tripper frame 10 in position to receive fluid underpressure from the four-way pilot operated valve 42 selectively throughconduits 43 and 44 is a conventional hydraulic motor 4-6. To move thetripper in one direction, the fluid is delivered to the hydraulic motor46 through pipe 43, and the fluid is delivered from the motor throughpipe 44 back to the four-way valve 42, thence through a pipe 47 and pipeto the tank 36 at atmospheric pressure.- The pipe 47 thus serves as anexhaust line for the valve 42. To reverse the tripper, the pilotoperated valve 42 is actuated to reverse the flow of fluid through thepipes 43 and 44 and hydraulic motor 46.

Communicating with pipe 41 is a pipe 48 which sup plies fluid underpressure to a conventional four-way pilot valve 4-9 which operates thevalve 42. Dogs 51 and 52, see Fig. l, are placed at desired limits alongthe tripper track 12 for engaging the valve 49 and thus reversing thedirection of tripper travel. The four-way pilot valve 49 communicateswith opposite sides of the pilot-operated valve 42 by means of pipes 53and 54, and communicates with the tank 36 by means of a pipe 56 andpipes 47 and'35; In the position shown in Fig. 7, valve 49 conductsfluid from pipe 48 to pipe 53 thence to one side of the pilot-operatedvalve 42 to operatethe same. Fluid from the opposite side of the valve42 and the fluid in the pipe 54, is conveyed through valve 49 to thepipe 56 and thence through pipes 47 and 35 to tank 36 at atmosphericpressure. The pipe 56 is in effect an exhaust line for the valve 49.When the pilot valve 49 is tripped to the opposite position, as shown inFig. 6, pressure is reversed through pipes 53 and 54, thus operating thevalve 42, and causing a reversal of the fluid flow through the motor 46and a reversal of the direction of tripper travel along the track 12.The pilot valve 49 has a blocked center portion 60 and does riot releasepressure atone side of the valve 42 until it is in position to applypressure at the opposite side thereof. Also, when the valve 42 is in thecenter position all of its ports are closed. In other words, there is noreversal of fluid until the operation of the valves is complete.Accordingly, there is no lag in the operation of the reversing mechanismas there is when mechanical means are employed to reverse the tripper.The blocked center portion 60 is provided with a cross connection 60awhich conveys the fluid from pipe 48 to pipe 53, and a cross connection60b which conveys the fluid to the pipe 56 from either of the pipes 53or 54 that is not connected to the supply pipe 48.

The hydraulic motor 46 drives an input shaft 58 of a worm gear speedreducer 59 through a flexible coupling 61. The speed reducer 59 has alow speed shaft 62 which is secured to a sprocket 63. The Wheels 11 ofthe tripper are mounted on axles 64 and 65 and secured to the axle 64 isa sprocket 66. The sprocket 63 drives the sprocket 66 through a chain67. While we show the sprocket 66 asbeing mounted on the axle 64 it willbe apparent that the sprocket could be mounted on axle 65, therebydriving the tripper through axle 65. The speed reducer arrangementbetween the hydraulic motor 46 and the tripper axle 64 or 65, as thecase may be, is employed so as to make it possible to use conventionaltypes of hydraulic or pneumatic motors.

Communicating with the pressure relief valve 38 is a pipe 68 whichconnects with a port 70 in the lower end of a valve chamber 69. A pipe71 communicates with the upper end of the valve chamber 69 through aport 71a. In normal operation, the valve chamber 69prevents the flow offluid from the pipe 68 to the pipe 71 which latter communicates withpipe 35. When for any reason it becomes necessary or desirable to stopmovement of the tripper along the track, a valve memher in the valvechamber 69 is moved downwardly by means of a handle 101 which isconnected to the valve member by a rod 105, thus connecting pipe 68 topipe 71 and permitting the fluid to flow back to the tank 36 atatmospheric pressure. With the valve memher 100 in the position justdescribed there is no driving force for propelling the tripper.

A pipe '72 connects pipe 68 to a fluid pressure cylinder 73 which ismounted on the tripper frame 10 by means of a suitable brackt75.Operating within the cylinder 73 is a piston 74 having a downwardlyextending pis ton rod 76. Mounted at the lower endof piston rod 76 are apair of gripping arms 77 and 77a which are adapted to engage the rail 12upon downward movement of thepiston rod 76. Mounted on the frame 10below the cylinder 73 is a bracket 78 having an opening 79 therein forreceiving the piston rod 76. A shoulder 81 is provided on the piston rod76 below thebracket 78. Surrounding the piston rod between thebracket 78and the shoulder 31 is a compression spring 82. An exhaust port 83 isprovided at the upper end of the cylinder 73 for releasing back pressuretherefrom as the piston 74 is moved upwardly by the fluid pressurereceived from line 72. i

As long as there is fluid of sufficient pressure within the cylinder 73acting on the piston 74, the shoulder 81 on the rod 76 is forcedupwardly against the compression spring 82 and the rail gripping arms 77and 7 711 are in the inoperative position. If for any reason there is arelease of pressure, such as would result when the handle 101 moves thevalve member 100 from between the ports 70 and 71a or when there is abreak in the hydraulic or pneumatic lines, or when a pump driving chainis broken, the compression spring 82 forces the piston rod 76 downwardlyand moves the rail gripping arms into engagement with the rail 12.

If the drive chain 67 should break, the tripper becomes a freerollingbody on the track so long as the pressure in the cylinder 73 issuflicient to hold the gripping arms 77 and 77a in the releasedposition. However, as the tripper gains velocity as it moves along itstrack in the direction of belt travel, the relative velocity of theconveyor belt around the pulley 17 decreases, thereby driving the pump31 at a slower speed. As a result, the hydraulic pressure from the pump31 decreases and the hydraulic motor then speeds up under a noloadcondition, thus further reducing the hydraulic pressure. By having aproper balance of pressure exerted by the spring 82 and piston 74 fornormal operating conditions, the gripping arms are automatically setupon release of pressure before the tripper would have gained sufficientspeed to cause any damage to the tripper and conveyor apparatus.

The valve member 100 is connected to a downwardly extending rod 86 andconnected to the lower end of rod 86 is a releasable connecting member87 having downwardly extending legs 85 and 85a. Each of the downwardlyextending legs is provided with a recess 88 adjacent the lower endthereof. Mounted on frame beneath the connecting member 87 are a pair ofvertically spaced brackets 89 and 91 having openings 92 and 93 thereinrespectively, for receiving a vertical rod 94. Extending laterally fromthe rod 94, adjacent to the upper end thereof, is a pin 96 which isadapted to fit in the recess 88 thereby releasably connecting the rod 86to the rod 94.

Secured to the lower end of the rod 94 by means of a set screw 97 is abracket 98. An opening 99 is provided in the outer end of the bracket 98for slidably receiving the lower end of the piston rod 76. When there isa release of pressure in the line 72 the rod 76 moves downwardly tooperate the gripping arms 77 and 77a, and the shoulder 81 engages thebracket 98 thereby moving the rods 94 and 86 downwardly and permittingfluid to flow through the valve chamber 69. With the valve member 100 inposition to connect pipe 68 to pipe 71, thefluid is recirculated to thetank 36 as hereinbefore described through pipe 35. It will be apparentthat if air pressure is employed instead of hydraulic pressure, thepipes 47, 71 and 35 would not be necessary and exhaust ports could besubstituted therefor.

Mounted on the frame 10 and spaced laterally from the lower portion ofrod 94 are a pair of vertically spaced brackets 102 and 103. Slidablymounted in the brackets 102 and 103 for vertical movementis a rod 104having .mounted adjacent the bottom thereof a U-shaped bracket 106.Mounted for rotation in the U-shaped bracket 106 is a roller 107.Extending outwardly from the frame 10. between the upper end of rod 104and rod 94 is a pin 108. Pivotally mounted on the pin 108 is a bar 109having one end thereof engaging the top of the rod 104 and the other endthereof engaging a collar 111 which is secured to the rod 94 by means ofset screw 112. Surrounding the rod. 94, between bracket 91 and thecollar 111 is, a compression spring 113 which biases the rod 94 upwardlyand positions the valve member 100 between the ports 70 and 71a thusblocking the flow of fluid through valve chamber 69. Positionedoutwardly of each of the dogs 51 and 52 is a bracket 114 having inclinedsurfaces 116 and 117 in positionto be engaged by the roller 107. As theroller 107 engages the inclined surface of the bracket 114, the rod 104is moved upwardly, pivoting the arm 109 and causing the collar 111 andthe rod 94 to be moved downwardly. Upon downward movement of the rod 94the valve member 100 is positioned below the ports 70 and 71a causingthe fluid to recirculate to the tank 36 thus releasing pressure withinthe cylinder 73. Upon release of pressure in the cylinder 73, the spring82 moves the rod 76 downwardly thereby causing the gripping arms 77 and77a to engage the rail 12 as shown in Fig. 4. It will thus be seen thatby providing the brackets 114 outwardly of the dogs 51 and 52 and thepressure release means associated therewith there is no possibility ofthe tripper running away. In other words the brackets 114, roller 107,rod 104, and the linkage to valve chamber 69 provides an extra safetydevice which prevents the tripper from running away. After the rod 104has been moved upwardly by the bracket 114, it is necessary to disengagethe rod 94 from the rod 36 before the tripper can be placed intooperation again. The rods 86 and 94 are disengaged by moving theconnecting member 87 out of engagement with the pin 96. The rod 86 isthen moved upwardly by the handle 101, thus positioning the valve member100 between the ports and 71a and blocking the flow of fluid from pipe68. The pressure is then built up in the system and the tripper is movedaway from the bracket 114. As the pressure builds up in the cylinder 73the rod 76 and shoulder 81 are raised thus releasing pressure on thebracket 98 and permitting the spring 113 to force the rod 94 upwardly.When the rod 94 is thus moved upwardly the pin 96 falls into the recess88 thereby connecting the rods 94 and 86.

When the valve member is moved manually to connect the ports 70 and 71athe spring 113 cannot force the valve member 100 into position betweenthe ports 70 and 71a due to the fact that the fluid is recirculated tothe reservoir 36 thus releasing pressure in the cylinder 73 and causingthe spring 82 to hold the bracket 98 and rod 94 in the down position. Itwill thus be seen that the handle 101 would have to be actuated to placethe apparatus back into operation.

From the foregoing it will be seen that we have devised an improvedautomatic tripper which has all the advantages of the trippersheretofore employed and one which requires very little maintenance andadjustments to keep the same in operation. By providing pneumatic orhydraulic means for propelling the tripper along the track and automaticmeans for stopping the tripper in the event there is a pressure failure,we have eliminated the chances of a tripper running away. Also, byproviding automatic means for reversing the fiow of fluids through thepropelling motor upon a predetermined distance of tripper travel, thereis a reversal of the tripper along the track without the necessity ofhaving to employ electrical or mechanical clutch means for reversing thesame.

While we have shown our invention in but one form, it will be obvious tothose skilled in the art that it is not so limited, but is susceptibleof various changes and modifications without departing from the spiritthereof, and we desire, therefore, that only such limitations shall beplaced thereupon as are specifically set forth in the appended claims.

What we claim is:

l. The combination with a conveyor belt tripper frame mounted on wheelsand having pulleys journaled thereon around which a conveying beltpasses and which are driven by said belt, of a fluid pressure pumpmounted on said frame in driven relation with one of said pulleys, meanssupplying fluid to said pump, a fluid pressure motor mounted on saidframe and connected in driving relation with said wheels, conduitscommunicating with opposite sides of said motor, a four-way valve havingan exhaust port and communicating with said conduits and said pump, saidvalve being operable to introduce fluid selectively under pressure tothe motor through one of said conduits and discharge fluid through theother of said conduits and said exhaust port, and a four-way pressureoperated pilot valve communicating with said pump and with the four-wayvalve to be operated for actuating the same upon a predetermineddistance of tripper travel, said pilot valve having an exhaust port andbeing constructed and arranged'for the operation thereof to be completedbefore there is a change of flow in the valve to be controlled.

2. The combination set forth in claim 1 in which the pilot valve isprovided with a blocked center portion having awe -22s cross connectionswhich convey fluid under pressure selectively from a source of supply toopposite sides of the four-way valve to be operated and exhaust thefluidfrom the four-way valve to be operated opposite the side thereofthat'pressure is applied.

3". The combination with a conveyor belt tripper frame mounted on wheelsfor rotation along rails and having pulleys journaledthereon aroundwhich a conveying belt passes andwhich are. driven by said belt; of afluidpressure pump mounted on said'frame in driven relation with one ofsaid pulleys, means supplying fluid to said pump, a fluid pressure motormounted on said frame in driving relationwith said wheels, conduitsconveyingfluid under pressure from said pump selectivelyto oppositesidesof the motor, a pressure relief valve in one of said; conduitsmaintaining a constant pressure therein, a rail gripping member attachedto saidfrarne and extendingdowriwardly t refr m n. pos t on to. e seqnef id d means actuating said rail gripping member upon a predetermineddecrease of pressure in said conduits andconcomitantly actuating othermeans which, release the pressure in saidconduits.

4. The combination, with a conveyor belt tripper frame mounted on wheelsfor rotation along rails and having pulleys journaled thereon aroundwhich a conveying belt passes and which are driven by said belt, of afluid pres sure pump mounted on said frame in driven relation with oneof said pulleys, means supplying fluid to said pump, a fluid pressuremotor mounted on said frame in driving relation with said wheels,conduits conveying fluid under pressure from said pump selectivelytoopposite sides of the motor, a pressure relief valve in one of saidconduits. maintaining a constant pressure therein, a rail grippingmember attached to said frame and extending downwardly therefrom inposition to engage one of said rails, a cylinder mounted on the frame,said cylinder communicating ad-. jacent the bottom. thereof with theconduits supplying fluid under pressure and being provided with anexhaust port adjacent the top thereof, a piston in said cylinder, apiston rod connecting said piston tov the, rail gripping member, andmeans associated with said rod, adapted upon a predetermined decrease ofpressure in said; cylinder to bias said rod downwardly and actuate saidrail gripping member. 7 A

5. The combination set; forth. in claim 4 in which the means for biasingthe rod downwardly upon a predeter mined decrease of pressure in thecylinder wmPrises a bracket secured to the frame below the cylinder andhaving an opening therein slidably receiving said rod, a shoulder onsaid rod beneath said bracket andacoxnpression spring surrounding saidrod between said bracket and said shoulder.

6 The combination with a conveyor belt tripper frame mounted on wheelsfor rotation along rails and having pulleys journaled thereon aroundwhich a conveying belt passes and which are driven by said belt, of afluid pressure pump mounted on said frame in driven relation with one ofsaid pulleys, means supplying fluid to said pump, a fluid pressure motormounted on said frame in driving relation with said wheels, conduitsconveying fluid under pressure from said pump selectively to oppositesides of the motor, a pressure relief valve in one. of said conduitsmaintaining a constant pressure therein, a rail gripping member attachedto said frame and extending down ardly therefrom and operable to engageone of said rails upon a predetermined decrease of pressure in saidconduits, a valve chamber mounted on the frame and having a pair ofvertically spaced ports therein, one of said ports being communicationwith the conduit conveying fluid under pressure and the other being anexhaust port, a valve member in said chamberdisposed to block the flowof fluid therethrough when positioned be tween said ports and; toexhaust; saidfluidwhen moved to connect salidports, andnieans movingsaid valve membet to connect said-port s, upp'n'a predetermined distanceof tripper travel;

' The combination set forth in claim 6 in which the means for moving thevalve member to connect, said'ports comprises a rod attached to saidvalve member and an operating handle attached to said rod for moving thesame. i v

8, The combination set forth in claim 6 in which the means for movingthe valve member to connectsaidports comprises a rod attached to thevalve member andextending downwardly therefrom a second rod mounted onsaid frame for vertical movement positioned laterally of the first,mentioned rod, a collar on the first mentioned rod, a linlcpivotallyrncunted on the. frame betweensaid e and. ha n Que endfia a n e t aid cela andthe other endthereof engaging the top of said second od. an m a hewe. d. o aid' ewns rod adapted to be actuated uponapredetermineddistance of tripper travel, and move the said secondrod upwardly.

9 The combination setforth in, claim 8 in which a con lpression. spring.surrounds the first mentioned rod beneath the collar, and a springabutment is mounted on said frame in position to engage'the bottom ofsaid spring, said spring biasing the valve member, upwardly to block theflow of fluid through thevalye chamber.

10. The combination set. forth in claim 8 in which the first mentionedrod is diyidedintodetachable sections,

11. lfor. use in actuating a rail gripping. member of a conveyor belttripper. mounted for rotation along rails and propelled by a fluidpressure nnit which is driven by a moving conveyor belt, a cylindermounted on said tripper above one of said rails, a conduit connectingthe fluid pressure unit to. the cyli der adjacent the bottom thereof,there being an exhaust, opening adjacent the top of said cylinder, apiston in said cylinder, a 'pistonrod connecting said piston to. saidrail gripping member, and means; adapted upon a predetermined decreaseof pressure. in said. cylinder to biassaid. rod downwardly and actuatesaid rail gripping member.

12. For. use in actuating a rail gripping member of a conveyor belttripper mounted for-rotation along rails, a a sr o ed. on a e a o e nef, s r s; a conduit supplying. fluid. under pressure, to the cylinderadjacent the bottom thereof, there being an exhaust opening adjacent thetop of said cylinder, a piston in said cylinder, a piston rodconnectingsaid pistonv to said rail gripping member, means adapted to.bias said rod down: e r an ac ua aid ra gripping emb upon release ofpressure infsaid cylinder, a valve chamber mounted on. the tripper andhaving a pair of vertically spaced, ports therein, one of said pcrt sbeing in communi; cation with" said conduit supplyihg'fluid underpressure. and the otherbeing an exhaust port, a valve member in saidvalve chamber disposed to block the, flow of fluid therethroughwhenpositioned between said ports and to, exhaust said fluid when movedto. connect said ports and means moving said valve member. to connectsaid ports] upon a predetermined distance of; tripper travel.

Re erenc s. Cited. th fil thi P n UNITED STATES PATENTS 758,810 BaldwinMay 3, 1904 1,575,655. Stinson Mar. 9 1 926 1,651,656. Yerkes Dec. 6,1927 1,937,077 West Nov. 28, 19.33 2,906,280 Schlueter June 25, 19352,081,465 Stewart et a1. May 25., 193.7 2,228,411 Sheridan Jan. 14, 1941

